Recently, the utilization of the biomass energy is pushed forward from the standpoint of cleaning the environment of the earth and decreasing the amount of discharged carbon dioxide. A fatty acid methyl ester obtained from fat and oil derived from plants is attracting attention as one of the biomass energy since the ester can be used for existing diesel engines without further treatments.
A fatty acid methyl ester obtained from waste food oils is being practically used in Japan. A fatty acid methyl ester obtained from plant oils such as rapeseed oil is in the stage close to the practical use in Europe and America.
As described above, fatty acid methyl ester is expected to be a fuel oil suppressing adverse effects on the environment and replacing gas oil. However, it is necessary that glycerol formed as a by-product during the production be utilized effectively. In particular, this is a great problem when the fatty acid methyl ester is produced in a great amount. For utilization of glycerol formed as a by-product, it is heretofore discussed that the glycerol might be sold in the market as a high purity glycerol after being treated in accordance with the processes of preliminary purification, distillation and purification similar to the processes heretofore conducted in the fat and oil chemical plants. However, it is the actual present situation that glycerol formed as a by-product is burned as fuel or for disposal since the above glycerol is expensive due to the small amount of production. Glycerol formed as a by-product can be supplied at a cost comparable to the cost of glycerol shipped from fat and oil chemical plants when the glycerol is produced in a great amount. However, since the demand and the supply of glycerol are already in the balanced condition in the market, it is worried that an additional supply of glycerol in a great amount would disturb the market (for example, “Biomass Handbook”, edited by the Japanese Society of Energy, 2002, pages 138 to 143). Although novel applications of glycerol have been sought for, the possibility of overcoming the problem in near future is small. Therefore, the biomaterial-derived diesel fuel described above is considered to be a biomass energy accompanied with the problem of the treatment of glycerol formed as a by-product.